(a) Field of the Invention
The present invention relates to a method and a system for controlling engine start of a hybrid vehicle configured to control engine start in a hybrid vehicle based on acceleration demanded power from a driver.
(b) Description of the Related Art
As oil prices increase and exhaust gas regulations tighten, eco-friendly demands and fuel efficiency improvements have become the focus of many automotive manufactures. Accordingly, vehicle manufactures have put forth increased efforts to develop technologies for reducing fuel consumption and decreasing exhaust gas emissions in order to meet eco-friendly demands and improve fuel efficiency.
In response to the above demands, the automotive manufactures have particularly focused interests and efforts toward development hybrid electric vehicles (HEV) which utilize a combination of power from an engine and power from a motor to achieve high degrees of fuel efficiency. As a result, hybrid vehicles have met purchase demands of many customers due to their high fuel efficiency and eco-friendly image.
FIG. 1, in particular, illustrates a conceptual configuration of a hybrid vehicle. Referring to FIG. 1, a hybrid vehicle (HEV) typically includes a transmission 22 for adjusting and determining a speed ratio between a driving shaft 12 and a wheel shaft 14. An electric motor 24 configured to transfer power to the driving shaft 12 via electric energy and regenerate energy via inertia from the vehicle during braking. An engine 26 generates power via fuel injection into one or more cylinders of the engine, and an engine-side clutch 28 transfers power from the engine 26 to the driving shaft 12 and cuts off the power of the engine 26 accordingly. Lastly, an engine starting/stopping motor 32 is configured to start and stop the engine 26. The engine starting/stopping motor 32 may be called an idle stop & go (ISG) or a hybrid starter & generator (HSG), as referred in a vehicle industry and thus for purposes discussed herein are thought of as one and the same.
As mentioned above, hybrid vehicles may run by appropriately via a combination of power from the engine 26 and from the electric motor 24. That is, the hybrid vehicle may run via the power from the engine 26 on a road, such as an expressway, in which a high speed is allowed, and via power from the electric motor 24 on a road in which traffic is congested or at lower speeds such as in the city.
As a result, hybrid vehicles run in an electric vehicle (EV) mode using only an electric motor when driving requires little torque or power, and run in a hybrid electric vehicle (HEV) mode using the electric motor and the engine together when driving requires a larger torque or power.
Hybrid vehicles run while appropriately switching between the EV mode and the HEV mode depending on a driving situation according to a characteristic thereof. For example, conditions under which the EV mode is switched to the HEV mode may include: (1) a driving demanded power (or acceleration demanded power) of a driver exceeds a discharge allowance maximum value of a battery; (2) a driving demanded power of a driver exceeds maximum power generable by the motor; (3) a driving demanded power of a driver exceeds a preset high-output driving demanded power value; and/or (4) a driving demanded power of a driver exceeds a preset low output driving demanded power for a predetermined time or longer.
It will be apparent to those skilled in the art that the driving demanded power of the driver under conditions (1) to (3) is considerably smaller than the driving demanded power of driver under condition (4). More specifically, the driving demanded power of the driver may be variously sensed. For example, the driving demanded power of the driver may be sensed through an output value variance (or variation ratio) of an accelerator pedal sensor (APS) according to manipulation of an accelerator pedal by the driver.
Conditions (1) to (3) are generally understood by those skilled in the art. However, condition (4) may be a selective mode switching condition. A reason for setting the mode switching condition, such as condition (4), may be as follows. That is, the driving condition is sufficient for operating within the EV mode, however it is necessary to more rapidly switch from the EV mode to the HEV mode by slightly decreasing an EV mode operating time (section) for a future battery SOC management control algorithm (charge/discharge management). Otherwise, the reason of setting the mode switching condition is that when a predetermined time (for example, 2.5 seconds, FIG. 2) passes after a driver of the hybrid vehicle steps on an accelerator pedal (or a driving demanded power of a driver starts to exceed a preset low-output driving demanded power), it is necessary to achieve an effective SOC management by charging the battery with an extra portion of the power from the engine by entering the HEV mode.
However, when condition (4) is applied to the hybrid vehicle as the mode switching condition, the EV mode may frequently switch to the HEV mode, thereby incurring repetitive switching. The reason is that the engine needs to be started while switching from the EV mode to the HEV mode as described above.
An exemplary situation in which a frequent mode switching may occur under mode switching condition (4) will be described below. For example, an accelerator pedal manipulation characteristic of a particular driver while operating the vehicle and analyzed through an operational characteristic of an accelerator pedal sensor (APS) may exhibit the characteristic illustrated in FIG. 2.
Referring to FIG. 2, section (a) of the APS is a section in which a driver steps on the accelerator pedal to thereby request acceleration so that an output value of the APS increases, section (b) of the APS is a section in which a driver uniformly steps on the accelerator pedal for acceleration at a fixed speed so that an output value of the APS is uniformly maintained, and section (c) of the APS is a section in which a driver releases the accelerator pedal for decelerated driving so that an output value of the APS decreases.
However, conventionally, since the output value of the APS decreases in section (c) of the APS due to the reason below, once the predetermined period of time (for example, 2.5 seconds, FIG. 2) passes after the driver initially steps on the accelerator pedal (that is, the driving demanded power of the driver starts to exceed the preset low-output driving demanded power), the vehicle switches to the HEV mode even though the driving mode needs to be in the EV mode, thereby negatively influencing fuel efficiency and the state of charge (SOC) management of the hybrid vehicle.
As described above, because of mode switching in condition (4), the engine is started and the vehicles switches to an HEV mode even though the driving mode should be in an EV mode because the output value of the APS decreases in section (c) of the APS in FIG. 2.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.